fix: control attrs better as described in issue #3277

src/awkward/_attrs.py

@@ -1,7 +1,9 @@
 # BSD 3-Clause License; see https://github.com/scikit-hep/awkward-1.0/blob/main/LICENSE
 from __future__ import annotations
 
+import weakref
 from collections.abc import Mapping
+from types import MappingProxyType
 
 from awkward._typing import Any, JSONMapping
 
@@ -42,3 +44,39 @@ def attrs_of(*arrays, attrs: Mapping | None = None) -> Mapping:
 
 def without_transient_attrs(attrs: dict[str, Any]) -> JSONMapping:
     return {k: v for k, v in attrs.items() if not k.startswith("@")}
+
+
+class Attrs(Mapping):
+    def __init__(self, ref, data: Mapping[str, Any]):
+        self._ref = weakref.ref(ref)
+        self._data = _freeze_attrs(data)
+
+    def __getitem__(self, key: str):
+        return self._data[key]
+
+    def __setitem__(self, key: str, value: Any):
+        ref = self._ref()
+        if ref is None:
+            msg = "The reference array has been deleted. If you still need to set attributes, convert this 'Attrs' instance to a dict with '.to_dict()'."
+            raise ValueError(msg)
+        ref._attrs = _unfreeze_attrs(self._data) | {key: value}
+
+    def __iter__(self):
+        return iter(self._data)
+
+    def __len__(self):
+        return len(self._data)
+
+    def __repr__(self):
+        return f"Attrs({_unfreeze_attrs(self._data)!r})"
+
+    def to_dict(self):
+        return _unfreeze_attrs(self._data)
+
+
+def _freeze_attrs(attrs: Mapping[str, Any]) -> Mapping[str, Any]:
+    return MappingProxyType(attrs)
+
+
+def _unfreeze_attrs(attrs: Mapping[str, Any]) -> dict[str, Any]:
+    return dict(attrs)

src/awkward/highlevel.py

@@ -18,7 +18,7 @@
 
 import awkward as ak
 import awkward._connect.hist
-from awkward._attrs import attrs_of, without_transient_attrs
+from awkward._attrs import Attrs, attrs_of, without_transient_attrs
 from awkward._backends.dispatch import register_backend_lookup_factory
 from awkward._backends.numpy import NumpyBackend
 from awkward._behavior import behavior_of, get_array_class, get_record_class
@@ -42,7 +42,7 @@
     unpickle_record_schema_1,
 )
 from awkward._regularize import is_non_string_like_iterable
-from awkward._typing import Any, MutableMapping, TypeVar
+from awkward._typing import Any, TypeVar
 from awkward._util import STDOUT
 from awkward.prettyprint import Formatter
 from awkward.prettyprint import valuestr as prettyprint_valuestr
@@ -337,7 +337,7 @@ def __init__(
         if behavior is not None and not isinstance(behavior, Mapping):
             raise TypeError("behavior must be None or a mapping")
 
-        if attrs is not None and not isinstance(attrs, MutableMapping):
+        if attrs is not None and not isinstance(attrs, Mapping):
             raise TypeError("attrs must be None or a mapping")
 
         if named_axis:
@@ -379,7 +379,7 @@ def _update_class(self):
         self.__class__ = get_array_class(self._layout, self._behavior)
 
     @property
-    def attrs(self) -> Mapping:
+    def attrs(self) -> Attrs:
         """
         The mutable mapping containing top-level metadata, which is serialised
         with the array during pickling.
@@ -390,14 +390,14 @@ def attrs(self) -> Mapping:
         """
         if self._attrs is None:
             self._attrs = {}
-        return self._attrs
+        return Attrs(self, self._attrs)
 
     @attrs.setter
     def attrs(self, value: Mapping[str, Any]):
         if isinstance(value, Mapping):
-            self._attrs = value
+            self._attrs = dict(value)
         else:
-            raise TypeError("attrs must be a mapping")
+            raise TypeError("attrs must be a 'Attrs' mapping")
 
     @property
     def layout(self):
@@ -1846,7 +1846,7 @@ def __init__(
         if behavior is not None and not isinstance(behavior, Mapping):
             raise TypeError("behavior must be None or mapping")
 
-        if attrs is not None and not isinstance(attrs, MutableMapping):
+        if attrs is not None and not isinstance(attrs, Mapping):
             raise TypeError("attrs must be None or a mapping")
 
         if named_axis:
@@ -1883,7 +1883,7 @@ def _update_class(self):
         self.__class__ = get_record_class(self._layout, self._behavior)
 
     @property
-    def attrs(self) -> Mapping[str, Any]:
+    def attrs(self) -> Attrs:
         """
         The mapping containing top-level metadata, which is serialised
         with the record during pickling.
@@ -1894,12 +1894,12 @@ def attrs(self) -> Mapping[str, Any]:
         """
         if self._attrs is None:
             self._attrs = {}
-        return self._attrs
+        return Attrs(self, self._attrs)
 
     @attrs.setter
     def attrs(self, value: Mapping[str, Any]):
         if isinstance(value, Mapping):
-            self._attrs = value
+            self._attrs = dict(value)
         else:
             raise TypeError("attrs must be a mapping")
 
@@ -2672,7 +2672,7 @@ def _wrap(cls, layout, behavior=None, attrs=None):
         return out
 
     @property
-    def attrs(self) -> Mapping[str, Any]:
+    def attrs(self) -> Attrs:
         """
         The mapping containing top-level metadata, which is serialised
         with the array during pickling.
@@ -2683,12 +2683,12 @@ def attrs(self) -> Mapping[str, Any]:
         """
         if self._attrs is None:
             self._attrs = {}
-        return self._attrs
+        return Attrs(self, self._attrs)
 
     @attrs.setter
     def attrs(self, value: Mapping[str, Any]):
         if isinstance(value, Mapping):
-            self._attrs = value
+            self._attrs = dict(value)
         else:
             raise TypeError("attrs must be a mapping")
 

tests/test_2757_attrs_metadata.py

@@ -25,7 +25,7 @@ def test_set_attrs():
     assert array.attrs == {}
 
     array.attrs = OTHER_ATTRS
-    assert array.attrs is OTHER_ATTRS
+    assert array.attrs == OTHER_ATTRS
 
     with pytest.raises(TypeError):
         array.attrs = "Hello world!"
@@ -52,7 +52,7 @@ def test_transient_metadata_persists():
     attrs = {**SOME_ATTRS, "@transient_key": lambda: None}
     array = ak.Array([[1, 2, 3]], attrs=attrs)
     num = ak.num(array)
-    assert num.attrs is attrs
+    assert num.attrs == attrs
 
 
 @pytest.mark.parametrize(
@@ -79,13 +79,13 @@ def test_single_arg_ops(func):
     # Carry from argument
     assert (
         func([[1, 2, 3, 4], [5], [10]], axis=-1, highlevel=True, attrs=SOME_ATTRS).attrs
-        is SOME_ATTRS
+        == SOME_ATTRS
     )
     # Carry from outer array
     array = ak.Array([[1, 2, 3, 4], [5], [10]], attrs=SOME_ATTRS)
-    assert func(array, axis=-1, highlevel=True).attrs is SOME_ATTRS
+    assert func(array, axis=-1, highlevel=True).attrs == SOME_ATTRS
     # Carry from argument exclusively
-    assert func(array, axis=-1, highlevel=True, attrs=OTHER_ATTRS).attrs is OTHER_ATTRS
+    assert func(array, axis=-1, highlevel=True, attrs=OTHER_ATTRS).attrs == OTHER_ATTRS
 
 
 @pytest.mark.parametrize(
@@ -134,15 +134,15 @@ def test_string_operations_unary(func):
             highlevel=True,
             attrs=SOME_ATTRS,
         ).attrs
-        is SOME_ATTRS
+        == SOME_ATTRS
     )
     # Carry from outer array
     array = ak.Array(
         [["hello", "world!"], [], ["it's a beautiful day!"]], attrs=SOME_ATTRS
     )
-    assert func(array, highlevel=True).attrs is SOME_ATTRS
+    assert func(array, highlevel=True).attrs == SOME_ATTRS
     # Carry from argument exclusively
-    assert func(array, highlevel=True, attrs=OTHER_ATTRS).attrs is OTHER_ATTRS
+    assert func(array, highlevel=True, attrs=OTHER_ATTRS).attrs == OTHER_ATTRS
 
 
 @pytest.mark.parametrize(
@@ -188,15 +188,15 @@ def test_string_operations_unary_with_arg(func, arg):
             highlevel=True,
             attrs=SOME_ATTRS,
         ).attrs
-        is SOME_ATTRS
+        == SOME_ATTRS
     )
     # Carry from outer array
     array = ak.Array(
         [["hello", "world!"], [], ["it's a beautiful day!"]], attrs=SOME_ATTRS
     )
-    assert func(array, arg, highlevel=True).attrs is SOME_ATTRS
+    assert func(array, arg, highlevel=True).attrs == SOME_ATTRS
     # Carry from argument exclusively
-    assert func(array, arg, highlevel=True, attrs=OTHER_ATTRS).attrs is OTHER_ATTRS
+    assert func(array, arg, highlevel=True, attrs=OTHER_ATTRS).attrs == OTHER_ATTRS
 
 
 def test_string_operations_unary_with_arg_slice():
@@ -220,16 +220,16 @@ def test_string_operations_unary_with_arg_slice():
             highlevel=True,
             attrs=SOME_ATTRS,
         ).attrs
-        is SOME_ATTRS
+        == SOME_ATTRS
     )
     # Carry from outer array
     array = ak.Array(
         [["hello", "world!"], [], ["it's a beautiful day!"]], attrs=SOME_ATTRS
     )
-    assert ak.str.slice(array, 1, highlevel=True).attrs is SOME_ATTRS
+    assert ak.str.slice(array, 1, highlevel=True).attrs == SOME_ATTRS
     # Carry from argument exclusively
     assert (
-        ak.str.slice(array, 1, highlevel=True, attrs=OTHER_ATTRS).attrs is OTHER_ATTRS
+        ak.str.slice(array, 1, highlevel=True, attrs=OTHER_ATTRS).attrs == OTHER_ATTRS
     )
 
 
@@ -262,13 +262,13 @@ def test_string_operations_binary(func):
             highlevel=True,
             attrs=SOME_ATTRS,
         ).attrs
-        is SOME_ATTRS
+        == SOME_ATTRS
     )
     # Carry from first array
     array = ak.Array(
         [["hello", "world!"], [], ["it's a beautiful day!"]], attrs=SOME_ATTRS
     )
-    assert func(array, ["hello"], highlevel=True).attrs is SOME_ATTRS
+    assert func(array, ["hello"], highlevel=True).attrs == SOME_ATTRS
 
     # Carry from second array
     value_array = ak.Array(["hello"], attrs=OTHER_ATTRS)
@@ -278,7 +278,7 @@ def test_string_operations_binary(func):
             value_array,
             highlevel=True,
         ).attrs
-        is OTHER_ATTRS
+        == OTHER_ATTRS
     )
     # Carry from both arrays
     assert func(
@@ -289,7 +289,7 @@ def test_string_operations_binary(func):
 
     # Carry from argument
     assert (
-        func(array, value_array, highlevel=True, attrs=OTHER_ATTRS).attrs is OTHER_ATTRS
+        func(array, value_array, highlevel=True, attrs=OTHER_ATTRS).attrs == OTHER_ATTRS
     )
 
 
@@ -298,38 +298,38 @@ def test_broadcasting_arrays():
     right = ak.Array([1], attrs=OTHER_ATTRS)
 
     left_result, right_result = ak.broadcast_arrays(left, right)
-    assert left_result.attrs is SOME_ATTRS
-    assert right_result.attrs is OTHER_ATTRS
+    assert left_result.attrs == SOME_ATTRS
+    assert right_result.attrs == OTHER_ATTRS
 
 
 def test_broadcasting_fields():
     left = ak.Array([{"x": 1}, {"x": 2}], attrs=SOME_ATTRS)
     right = ak.Array([{"y": 1}, {"y": 2}], attrs=OTHER_ATTRS)
 
     left_result, right_result = ak.broadcast_fields(left, right)
-    assert left_result.attrs is SOME_ATTRS
-    assert right_result.attrs is OTHER_ATTRS
+    assert left_result.attrs == SOME_ATTRS
+    assert right_result.attrs == OTHER_ATTRS
 
 
 def test_numba_arraybuilder():
     numba = pytest.importorskip("numba")
     builder = ak.ArrayBuilder(attrs=SOME_ATTRS)
-    assert builder.attrs is SOME_ATTRS
+    assert builder.attrs == SOME_ATTRS
 
     @numba.njit
     def func(array):
         return array
 
-    assert func(builder).attrs is SOME_ATTRS
+    assert func(builder).attrs == SOME_ATTRS
 
 
 def test_numba_array():
     numba = pytest.importorskip("numba")
     array = ak.Array([1, 2, 3], attrs=SOME_ATTRS)
-    assert array.attrs is SOME_ATTRS
+    assert array.attrs == SOME_ATTRS
 
     @numba.njit
     def func(array):
         return array
 
-    assert func(array).attrs is SOME_ATTRS
+    assert func(array).attrs == SOME_ATTRS

tests/test_2770_serialize_and_deserialize_behaviour_for_numba.py

@@ -19,7 +19,7 @@ def test_ArrayBuilder_behavior():
     SOME_ATTRS = {"FOO": "BAR"}
     builder = ak.ArrayBuilder(behavior=SOME_ATTRS)
 
-    assert builder.behavior is SOME_ATTRS
+    assert builder.behavior == SOME_ATTRS
     assert func(builder).behavior == SOME_ATTRS
 
 

tests/test_2806_attrs_typetracer.py

@@ -22,7 +22,7 @@ def test_typetracer_with_report():
     form = layout.form_with_key("node{id}")
 
     meta, report = typetracer_with_report(form, highlevel=True, attrs=SOME_ATTRS)
-    assert meta.attrs is SOME_ATTRS
+    assert meta.attrs == SOME_ATTRS
 
     meta, report = typetracer_with_report(form, highlevel=True, attrs=None)
     assert meta._attrs is None
@@ -44,5 +44,5 @@ def test_function(function):
             "z": [[0.1, 0.1, 0.2], [3, 1, 2], [2, 1, 2]],
         }
     )
-    assert function(array, attrs=SOME_ATTRS).attrs is SOME_ATTRS
+    assert function(array, attrs=SOME_ATTRS).attrs == SOME_ATTRS
     assert function(array)._attrs is None

tests/test_2837_ufunc_attrs_behavior.py

@@ -14,15 +14,15 @@ def test():
 def test_unary():
     x = ak.Array([1, 2, 3], behavior={"foo": "BAR"}, attrs={"hello": "world"})
     y = -x
-    assert y.attrs is x.attrs
+    assert y.attrs == x.attrs
     assert x.behavior is y.behavior
 
 
 def test_two_return():
     x = ak.Array([1, 2, 3], behavior={"foo": "BAR"}, attrs={"hello": "world"})
     y, y_ret = divmod(x, 2)
-    assert y.attrs is y_ret.attrs
-    assert y.attrs is x.attrs
+    assert y.attrs == y_ret.attrs
+    assert y.attrs == x.attrs
 
     assert y.behavior is y_ret.behavior
     assert y.behavior is x.behavior